The present invention relates to a process for the removal of undesirable materials from liquid systems and more particularly to a process for the removal of unreacted raw materials and unwanted by-products from liquid systems. The process comprises the delivery of a compressed, inert gas through the pores of a sintered porous sparger element and into a liquid system in the form of very small gas bubbles, referred to hereinafter as micro bubbles.
It is well-known to utilize inert gas sparging or stripping for removal of unreacted raw materials and unwanted by-products from chemical reactors and various processing tanks, such as pressure reactors, mixing or blending tanks and holding tanks. Stripping effectiveness is dependent upon good mass transfer between the inert gas and the liquid; typically, the higher the gas-liquid contact, the more efficient is the stripping.
Conventional sparger systems consist of an inert gas being dispersed into a liquid tank by means of nozzles, small holes in straight pipes or perforated rings or plates. To maintain a small gas bubble size, to prevent the gas bubbles from coalescing, and to maximize gas dispersion in the liquid, these conventional sparging systems depend, to a large extent, upon agitation, thereby necessitating the use of impellers, turbine impeller mixers or the like. The stripping effectiveness of these systems is also dependent on the volumetric flow rate and velocity of the stripping gas, orifice size and pressure drop across the orifice, as well as the physical properties (surface tension, density, viscosity) and temperature of the liquid mass to be stripped. Stripping effectiveness may be determined by the total length of time and total amount of inert gas necessary to achieve a product quality target. Product quality targets include such factors as removal of volatile materials to meet a flash point or removal of water from a reaction product.
Existing conventional sparging systems have certain limitations resulting in lengthened cycle time to obtain the necessary product quality targets and excessive use of the stripping gas. These limitations are particularly evident when conventional sparging techniques are utilized in liquid systems having high viscosities as such systems are much more difficult to strip than low viscosity liquids. As used in this specification and in the appended claims, the phrases "viscous liquid systems" and "systems having a high viscosity" are meant to describe those system or compositions having a viscosity greater than about 200 Cst., and typically greater than about 350 Cst., at 100.degree. C., for example, from about 750 Cst. to about 2,000 Cst. at 100.degree. C. Liquid systems having high viscosities include, but are not limited to, liquid compositions which are adapted for use as additives in oleaginous compositions such as fuels and lubricating oils. Among such high viscosity liquids there may be mentioned ashless and ash-containing dispersants such as borated and unborated polyisobutylene succinimides; anti-oxidant, anti-wear and/or anti-corrosion additives such as zinc dialkyldithiophosphates (ZDDP); and multi-functional viscosity modifiers, such as a blend of ethylene-propylene copolymer succinic anhydride and polyisobutylene succinic anhydride which has been aminated and then sulfonated.
The use of sintered porous materials to enhance sparging is also well known. For instance, porous spargers have been employed in aeration processes to diffuse air or other gases into various liquids (see generally U.S. Pat. Nos. 1,405,775, 2,639,131, 3,970,731, 4,105,725, 4,261,932, and 4,655,915). Additionally, porous elements have been used in the carbonation of liquids (U.S. Pat. Nos. 2,250,295 and 3,958,945). Further, as disclosed in U.S. Pat. Nos. 4,399,028 and 4,735,709, porous spargers have been effective in froth flotation systems.